High-pressure discharge lamps, such as sodium high-pressure discharge lamps, usually have discharge vessels of an aluminum oxide ceramic; metal halide discharge lamps usually have discharge vessels of quartz glass. High-power lamps of these types, that is, lamps in the over 100 W power rating range, for example 150 W, 250 W, and higher, require stable holders or mounts within the bulb to securely retain the discharge vessel therein. Such holders or mounts may include a multiplicity of components or elements. The discharge vessel should be retained in a predetermined position with respect to the mount since, frequently, the discharge vessel is to be operated in conjunction with a reflector so that the position of the discharge vessel, and the light generated therein with respect to the reflector, becomes critical.
Ceramic discharge vessels have a very substantial temperature coefficient of expansion. The operating temperature of such lamps is in the order of about 1000.degree. C. The problem arises that, due to the high operating temperature, differential expansion in operation between the discharge vessel and a metallic mount, and a glass outer bulb, has to be compensated. It is desirable to retain the axial orientation of the discharge vessel of such lamps in order to retain a predetermined position with respect to a possible reflector.
The arrangement to retain the discharge vessel in a secure and reliable position within the lamp is complicated by also providing an electrical connection to the electrodes of the discharge vessel. In the past, it was customary to separately provide for maintenance of the position of the discharge vessel in the outer bulb and for the electrical connection.
The discharge vessel, preferably, should be so retained within the bulb that it not only will retain a predetermined position, so that it can be located in a reflector, but also not be subject to excursion from the position due to vibration, while being protected against shock.
U.S. Pat. No. 4,254,355, Taylor, provides a mount of a ceramic arc tube on a support rod attached to one lead-in within an outer vitreous envelope in such a manner that expansion of the ceramic arc tube is possible. The inlet lead at one end of the arc tube is fastened to the support rod, which serves also as a conductor. At the other end, the inlet lead extends through an insulating bushing supported from the rod, and connected by a curved flexible conductor to the other lead-in located within the outer envelope. Differential thermal expansion is accomodated by sliding of the inlet lead through the bushing and, at the other end, by flexing of the conductor. The curved conductor is located in an open, approximately 180.degree. loop of thin wire, or metal foil. The arrangement permits expansion under heating; it does not, however, dampen excursion due to vibration.
Heat expansion of the discharge or arc vessel can be accepted by an axially arranged loop of a support wire secured to a holder or mount, see U.S. Pat. No. 3,882,346. The electrical connection between the mount and the current supply is provided by an elastic metal ribbon which at the same time is intended to dampen oscillations or vibrations. The plane of the metal ribbon is, however, placed in the longitudinal axis of the lamp so that vibrations transverse to the axis of the lamp are not damped, thereby decreasing the optical characteristics of the lamp when associated with a reflector.